(a) Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a cooling structure for a secondary battery module having a plurality of unit batteries.
(b) Description of the Related Art
Unlike a primary battery, a secondary battery may be recharged. Lower power batteries are used for various portable electronic devices such as cellular phones, laptop computers, and camcorders. Bulk size batteries are used as the power source for motor drive, such as in hybrid electric vehicles.
Depending on their external shape, secondary batteries may be classified into different types, for example, prismatic and cylindrical batteries. When they are used for machines requiring a high power source such as the hybrid electric vehicles, secondary batteries may be in the form of a high power secondary battery module.
A secondary battery module is formed by serially connecting several secondary batteries (“unit battery”). Each of the unit batteries includes an electrode assembly in which a separator is interposed between a positive electrode and a negative electrode. The electrode assembly is inserted into a container, and a cap assembly is assembled with the container to seal the container. If the unit battery is a prismatic type battery, the cap assembly includes a positive terminal and a negative terminal extending from the inside to the outside of the container and electrically connected to a positive electrode and a negative electrode, respectively.
In addition, the positive and negative terminals of one unit battery are arranged to alternate with the positive and negative terminals of an adjacent unit battery. The unit cells are electrically connected to each other to form the secondary battery module by fastening a conductive adaptor to the negative and positive terminals with screw threads on their outer surface.
Since the secondary battery module connects several to tens of unit batteries to form one battery module, there is a need to efficiently dissipate heat generated from each unit battery. In particular, when the secondary battery module is used for vehicles such as electric vehicles and hybrid electric vehicles, the heat dissipation is of significant importance.
If the heat dissipation does not occur properly, the temperature of the secondary battery module may excessively increase due to the heat generated from each unit battery. Accordingly, the secondary battery module and the unit driven by the secondary battery module may malfunction.
In addition, if the secondary battery module includes prismatic type unit batteries, it is more likely to generate excessive heat due to the structural characteristics of the prismatic type.
Accordingly, a cell barrier may be disposed between unit batteries. The space formed between unit batteries by the cell barrier is used not only for cooling unit batteries but also for preventing distortion due to heat expansion of the unit batteries.
However, such a cooling mechanism for secondary battery modules may cause an uneven temperature difference between unit batteries since the amount of cooling air supplied to the space between unit batteries may vary.
Accordingly, the secondary battery module is not able to maximize its characteristics such as charge-discharge characteristic, decreasing the efficiency of the modules.